Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
Author: Subject: Salting out
guy
International Hazard
*****




Posts: 982
Registered: 14-4-2004
Location: California, USA
Member Is Offline

Mood: Catalytic!

[*] posted on 20-9-2006 at 18:24
Salting out


Which salts are suitable for salting out ethanol (from denatured alcohol)? I've tried some salts like NaCl and MgSO4 and they didn't work.



View user's profile View All Posts By User
not_important
International Hazard
*****




Posts: 3874
Registered: 21-7-2006
Member Is Offline


[*] posted on 20-9-2006 at 22:28


Common salt is the preferred. I've used it with ethanol and methanol, remember that the alcohol is the majority liquid so it might be better to say that you are salting out the water. I just dumped in enough salt to leave a little solid after it had sat for a day.

If you use dehydrated MgSO4, then you're not even salting out. In cooler weather I use NaSO4 for the first dehydration, as it hols 2 to 3 times as much water per gram vs MgSO4 and is easier to dehydrate afterwards. Add enough excess to keep the crystals loose, stir it for 10 minutes or so.
View user's profile View All Posts By User
chromium
National Hazard
****




Posts: 284
Registered: 27-6-2005
Member Is Offline

Mood: reactive

[*] posted on 21-9-2006 at 01:19


IIRC potassium carbonate is most efective. It separates water almost completely.
View user's profile View All Posts By User
matei
Hazard to Others
***




Posts: 205
Registered: 16-9-2006
Member Is Offline


[*] posted on 21-9-2006 at 08:42


What exactly do you mean by "salting out ethanol" ? If you want to dehydrate it, use a dessicant like anh. MgSO4 or anh. Na2CO3.
"Salting out" with NaCl is used when you want to decrease the solubility in water of fairly water-soluble organic substances, so they can be better extracted with an organic solvent (like ether or benzene).
View user's profile View All Posts By User
YT2095
International Hazard
*****




Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline

Mood: within Nominal Parameters

[*] posted on 21-9-2006 at 09:57


it would also require that you know the denaturing agent too.
I have 100% ethanol, but it`s denatured with MEK.
desalt that Sucker! :P

common denatuting agents range from Meoh, Pyridine, MEK, Denatonium benzoate.

oh yeah, and this purple Dye stuff that I havent figured out yet, but Chlorine will remove the color.

[Edited on 21-9-2006 by YT2095]




\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
View user's profile View All Posts By User
chromium
National Hazard
****




Posts: 284
Registered: 27-6-2005
Member Is Offline

Mood: reactive

[*] posted on 21-9-2006 at 11:05


Quote:
Originally posted by matei
"Salting out" with NaCl is used when you want to decrease the solubility in water of fairly water-soluble organic substances, so they can be better extracted with an organic solvent (like ether or benzene).


Salting out can also force liquid into two separate phases - one mostly water with dissolved salt and another mostly organic liquid with relatively small amount of water and dissolved salt. This can easily be demonstrated in case of acetone+water or ethanol+water but in last case i am not sure if NaCl does the thing. K2CO3 does.

Of course if initial post is about removing denaturating agent then this is entirely different question and salting out is not (probably) the way that works.
View user's profile View All Posts By User
matei
Hazard to Others
***




Posts: 205
Registered: 16-9-2006
Member Is Offline


[*] posted on 22-9-2006 at 03:00


That's true, but in that case the two liquids must be inmiscible (or only partially miscible). The NaCl added increases the density of the aqueous layer and the two layers can be readily separated. It obviously won't work for ethanol-water because they are fully miscible.
View user's profile View All Posts By User
Nicodem
Super Moderator
*******




Posts: 3986
Registered: 28-12-2004
Member Is Offline


[*] posted on 22-9-2006 at 03:13


Being unsure whether saturated brine and ethanol mix or just form a biphasic system, I just tried it. I found out they mix with some NaCl precipitation. Therefore, brine and ethanol do not behave like brine/isopropanol or brine/acetone which rather form two layers.
I do know saturated NaOH(aq) does not mix with ethanol, but I don't know which other salts have such properties. It does sound reasonable that the saturated solutions of hygroscopic salts would prefer to form two layers, so K2CO3 might indeed do so. If anybody knows of others salts capable of behaving similarly it would be interesting to hear about it.

Edit:
Matei, full miscibility is no requisite for the "salting out" effect. Even though acetone is miscible with water in all proportions, it is not fully miscible in all proportions with water solutions of NaCl. Obviously, since a water solution of NaCl is not water, it has very different properties.

[Edited on 22-9-2006 by Nicodem]




…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)

Read the The ScienceMadness Guidelines!
View user's profile View All Posts By User
sonogashira
International Hazard
*****




Posts: 555
Registered: 10-9-2006
Member Is Offline


[*] posted on 22-9-2006 at 03:29


"saturated NaOH(aq) does not mix with ethanol"
Nicodem, does this mean that if i add 95% ethanol to a saturated sodium hydroxide solution i can get 100% ethanol?
View user's profile View All Posts By User
chromium
National Hazard
****




Posts: 284
Registered: 27-6-2005
Member Is Offline

Mood: reactive

[*] posted on 22-9-2006 at 03:56


Russian "Spravatshnik himika" Tom II has some data about equilibrum in ethanol-water-salt mixtures at various temperatures and concentrations.

Most salts DO NOT force this liquid into two separate phases but some do. Best results are with K2CO3 at temperature 23 ... 26C. Upper layer is 90% ethanol and 0.095% K2CO3, lower 0.3% Ethanol and 53.6% K2CO3.

With KOH upper layer was about 55 ... 59% ethanol with 30% KOH while lower layer was less than 1% EtOH with 52.8% KOH. Other salts that worked almost as well were MnSO4, (NH4)2SO4.

Na2CO3 was somewhat better than others but not as good as K2CO3. Na2SO4 too caused separation but was weaker than others.

If someone is interested i can upload that table but almost all usefull data is already here.

Another book (that was something about wood products) mentioned that methanol can be forced from aqueous mixture to upper layer by means of K2CO3 but i have no more data about this.


[Edited on 22-9-2006 by chromium]
View user's profile View All Posts By User
Nicodem
Super Moderator
*******




Posts: 3986
Registered: 28-12-2004
Member Is Offline


[*] posted on 22-9-2006 at 04:18


Thanks Chromium, for the interesting data. If there are data for other such ternary systems for other solvents as well, it might be usefull if you could scan the tables and upload them.

Quote:
Originally posted by sonogashira
"saturated NaOH(aq) does not mix with ethanol"
Nicodem, does this mean that if i add 95% ethanol to a saturated sodium hydroxide solution i can get 100% ethanol?


Obviously you can not get 100% ethanol doing so. Biphasic systems are dynamic systems ending up in partitition equilibriums (see Chromium's post above). Therefore by separating the ethanolic layer you would obtain a solution still containing some water, but additionally also some NaOH (which is additionally in the protolytic equilibrium with NaOEt). You would thus need to distill the collected ethanolic phase, which would utmost yield the ethanol/water azeotrope (96% ethanol). To obtain absolute ethanol you would need to further dry such a solution up until it would only be a solution of sodium ethoxyde in ethanol. This can be done by passing the solution trough a vertical column packed with solid NaOH (the saturated NaOH(aq) drops at the bottom while at the top you collect the saturated NaOEt/EtOH solution).

You can read more details about this topic in this (long) thread (if you have the patience):
https://sciencemadness.org/talk/viewthread.php?tid=2656&page...




…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)

Read the The ScienceMadness Guidelines!
View user's profile View All Posts By User

  Go To Top